Childhood Stress Boosts Harmful Brain Hormone

Neglect and abuse during early childhood can cause memory loss and impaired cognitive abilities later in life by boosting the production of a hormone
that harms the brain's learning and memory center, scientists
said Monday.

In an experiment involving laboratory rats, researchers at
the University of California at Irvine's College of Medicine
showed that these stress-related dysfunctions were caused by a
brain hormone called corticotropin-releasing hormone (CRH).

Until now, scientists had assumed that steroid stress hormones
produced by the adrenal glands were responsible.

Dr. Tallie Baram, who led the study, said pinpointing the
mechanism at work could lead to new types of treatments for
stress-related damage to the brain. The study appears in the
Proceedings of the National Academy of Sciences.

The researchers studied what happened in the brains of rats
in an attempt to gain a better understanding of how stress in
early childhood, including emotional neglect and abuse,
produces enduring negative consequences in people.

"It's been shown in children and infants and also in animal
models that chronic, early-life stress leads to a decline in
cognitive function, particularly cognitive function that's
related to the part of the brain called the hippocampus," Baram
said in an interview.

"That part of the brain is responsible for learning and
memory. What's been really not clear is how that happens."

Cell Death and Memory Impairment

Baram's team used a single injection of CRH, a hormone that
regulates the nervous system's responses to stress, to mimic
early-life stress in rats that were about two weeks old.

The rats given the injection experienced significant brain
cell death — a loss of between one-tenth and one-fifth of the
cells in a section of the hippocampus associated with
stress-related damage.

Rats injected with the hormone were less able to perform
spatial memory and object-recognition tests later in life than
rats that did not receive the injections.

While the injections were given only once early in life,
cell death in the hippocampus and memory problems worsened with
age, the study found.

"What we are finding is that not only are we killing cells
in the hippocampus, but there's also reorganization — new
connections to the existing cells that make them more
vulnerable," Baram said. "We create, if you will, a vicious
cycle in which stress early in life can have very persistent
effects throughout life."

The researchers ruled out steroid stress hormones — whose
levels shoot up during stressful events — as responsible for
the cell death. They said rats that had been altered to prevent
them from producing these adrenal hormones still showed the
memory loss and cell death produced by the CRH injection.

Baram said if scientists can find a method to block the
impact of CRH on the brain, it would be possible to create new
ways to prevent cognitive impairment later in life when
treating certain human stress-related disorders.